Modifiable areal unit problem

The modifiable areal unit problem (MAUP) is a source of statistical bias that can radically affect the results of statistical hypothesis tests. It affects results when point-based measures of spatial phenomena (e.g., population density) are aggregated into districts. The resulting summary values (e.g., totals, rates, proportions) are influenced by the choice of district boundaries. For example, census data may be aggregated into census enumeration districts, or postcode areas, or police precincts, or any other spatial partition (thus, the "areal units" are "modifiable").

The issue was recognized in 1934[1] and later described in detail by Stan Openshaw, who lamented that "the areal units (zonal objects) used in many geographical studies are arbitrary, modifiable, and subject to the whims and fancies of whoever is doing, or did, the aggregating."[2]